III.] LIFE AND DEATH. 1 29 



course of events as described by Gotte, and he is probably cor- 

 rect in his interpretation. This is the real death of the Ortho- 

 nectides, and if we regard them as low primitive forms (Mcso- 

 zoa), here for the first time in the ascending series we meet 

 with natural death. But the causes of this are scarcely so clear 

 as Gotte seems to think when he ascribes it to the effect of 

 reproduction — an effect which is ' not only empirically neces- 

 rary, but absolutely unavoidable.' Such a necessity is explained 

 by the fact that the endoderm consists entirely of germ-cells. 

 Now the life of the organism, being dependent upon the mutual 

 action of both layers, must cease as soon as the whole endoderm 

 is extruded during reproduction. 



Arguments such as these pass over the presence of a meso- 

 derm ; but apart from this omission, it does not appear to me 

 so self-evident from a purely physiological standpoint, that the 

 ectodermal sheath with its muscle layer must die after the ex- 

 trusion of the germ-cells. 



In those females to which Gotte refers in this passage, the 

 whole sheath remains at first quite uninjured, with the ex- 

 ception of a small cap at the anterior end, which is pushed 

 off to give exit to the ova ; and inasmuch as the sheath 

 continues to swim about in the nutritive fluids after this has 

 taken place, the proof is at any rate wanting that it cannot 

 support itself quite as well as before, although it has lost the 

 germ-cells. 



Then why does it die ? My answer to this is simple : — be- 

 cause it has lived its time ; because its length of life is limited to 

 a period which corresponds with the time necessary for com- 

 plete reproduction. The physical constitution of the body is so 

 regulated that it remains capable of living until the extrusion 

 of the reproductive cells, and then dies, however favourable 

 external conditions may be for its further support. 



The correctness of this explanation is shown by a considera- 

 tion of the males and the second form of females ; for in these 

 cases the body falls to pieces, not as a consequence of repro- 

 duction, but as a preparation for it ! 



Gotte only mentions the second female form in a note, in 

 which he says, it appears ' that in the second female form of 

 these animals the whole body breaks into many pieces, and the 

 superficial layer gradually atrophies, so that it dies before the 



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